Symptoms Your Furnace Burners Are Dirty And Needs Cleaning

A dirty furnace burner can result in many furnace problems. Indeed, you may ultimately not get any heat from the furnace or the appliance may go out altogether. Even worse, dirty furnace burners put you and your family at risk of gas poisoning as a partially blocked burner can result in incomplete burning. Therefore, you must be careful to prevent or otherwise fix dirty burners promptly.

This guide explains everything you need to know about furnace burners, focusing on the dangers of dirty burners and how to clean your burners.

What is a Furnace Burner?

The furnace burner is a component of the furnace where fuel from the gas lines mixes with oxygen-rich air, and the two burn to generate the heat necessary to keep your home warm and toasty. Furnace burners come in many forms.

For instance, some burners have a unique chamber known as the pre-mixer where cold air mixes with fuel before the mixture is introduced into the burner. Pre-mixers ensure better combustion, thus more efficient heating. However, most furnace burners don’t have this feature.

Furnace burners come in many styles, from gas and oil burners to propane burners. Depending on the design, a furnace may have one, two, or more burners. Two-burner furnaces are known as dual-burners, while those with more burners are known as multi-burner furnaces. 

Where is the Furnace Burner Located?

The standard up-flow furnace burner is located on the floor of the top compartment of the furnace. If you can locate the heat exchanger, the burner should be right below it. However, downflow and horizontal flow burners are located differently.

Generally, downflow burners are found in the bottom compartment of the furnace, while horizontal flow burners are located where air exits the furnace.

How Do I Know if My Furnace Burners are Dirty?

Fortunately, it’s not too difficult to know when the furnace burners are dirty. You want to keep an eye out for the following signs;

Short cycling

One of the first signs of dirty furnace burners is short cycling, i.e., the burners light for a few seconds then go out abruptly. Sometimes the burners may light up to a few minutes before going out. However, it rarely lasts more than three minutes.

Although this can also point to dirty filters that need cleaning/replacing, blocked burners are another common culprit. The reason is that the flame doesn’t get sufficient fuel to keep burning when the burners are partially blocked.

Difficulty maintaining the desired temperature setting

You’ll find it difficult to attain and maintain the desired thermostat setting if your burners aren’t letting enough gas through. You may momentarily get to the desired setting. However, keeping the home at that temperature for an extended period becomes a major challenge.

The good news is that it’s easy to tell when your furnace is struggling to reach the desired temperature setting. For one, you’ll feel colder than usual. Additionally, you can check the thermostat to see if you’re hitting your targets. If not, the burners could be blocked.

A yellow or orange flame

You probably saw this coming. A normal furnace flame is blue and stable. So, when the flame color changes, you know something is up. A common reason is incomplete burning, which essentially means the flame isn’t getting sufficient or oxygen-rich combustion air.

Blocked burners can be the main reason for the low air supply inside your burner. Obviously, you also want to check whether the vents are blocked. However, if everything else seems fine, the burners are likely the source of the problem.

Strange, loud noises 

Strange loud noises aren’t always the first sign of dirty furnace burners. So, we recommend considering other symptoms before listening out for the sounds. However, if you hear a loud banging noise, like a small explosion, when the furnace starts, then you may have blocked burners.

The loud “bang” is usually because the flame swells every time the gas forces its way through the dirt buildup. Besides the banging sounds, you may also hear sharp hissing sounds. You’ve likely heard the same sounds when you have a tire puncture. Again, it’s a sign that the gas is forcing a way out through a narrow, restricted path.

Reduced indoor air quality 

You may occasionally notice that your indoor air isn’t as clean as you’d like. Maybe you can see more floating debris, or the air smells musty. Or maybe there’s more dust than usual. You may even see the dust settling on your furniture and other items.

While this may point to damaged or worn filters, it can also signify filthy, clogged burners. Perhaps the black carbon debris is coming from accumulated dirt within the burner.

Strange odors from the furnace

We’ve already mentioned unusual odors as a sign of possible burner blockage. However, we must stress that the odors are dangerous if promptly addressed. These smells typically result from the burning process.

 Maybe the burner is clogged with pet dander, hairs, small insets, and cobwebs. This is common, especially at the onset of the heating season, if you skip seasonal tune-up. So, you may smell rubber, oil, or smoke when the furnace runs. It’s advisable to stop the heating and check whether the burners are blocked.

The furnace doesn’t come ON

Finally, the furnace may refuse to come ON altogether if you don’t clean the burners on time. This usually happens for two reasons. First, fuel cannot come out of the burner orifices if the burner is completely blocked. So, the burner can’t light. When this happens, the furnace’s lockout mechanism will engage after 3-5 ignition attempts, requiring a physical reset.

Secondly, an obstructed burner can result in a small flame that’s sucked into the burners. Furnaces consider this an overheating risk and will consequently shut down to avert further risk.

What Causes Dirty Furnace Burners?

Dirt builds up on furnace burners in three main ways – naturally, via air circulation, and through wear and tear.

  • Naturally: Natural dirt buildup on the furnace happens in all furnaces and on all parts of the furnace – even when the furnace isn’t running. Dust will settle on the various parts, and small insects can get into the burner area and the orifices. You may even find mold in the burner compartment. It’s completely natural, especially under poor furnace maintenance.
  • Through air circulation: However, the biggest cause of dirt buildup when the furnace is running is air circulation. Furnaces work by moving indoor air into the burner for heating then pushing the warm air out back into the room, and the cycle continues. If the filter is compromised thus unable to trap the airborne elements in return air, the particles will find their way into the burner compartment.
  • Wear and tear: Finally, the burners can also accumulate debris from wear and tear. For instance, rusting components can cause debris in and around the burner. Corrosion can also cause debris.

What Happens if Furnace Burners are Dirty?

Dirty furnace burners can cause all kinds of problems. However, the two most common impacts are health and performance-related.

  • Health impacts: Since the furnace’s filters are located on the return air side, all debris and dust in the burner compartment usually end up in indoor air. This can cause health problems, such as asthma aggravation.
  • Impacts on furnace performance: Blocked furnace burners can cause weak, yellow flames, resulting in poor, inefficient heating. Or, worse, it can cause the furnace to go off altogether.
  • Higher energy bills: Finally, blocked burners can also cause the furnace to run harder and longer, thus increasing energy bills.

How Often Do Furnace Burners Need to Be Cleaned?

Generally, you only need to clean the furnace burners yearly during the annual furnace tune-up. The best time for an annual tune-up is early fall. This allows you to fully prepare for winter and avoid any surprises.

However, you may need to clean the furnace more frequently depending on where you live and the appliance’s age.

How Do You Clean a Dirty Furnace Burner (Step-by-Step)

Fortunately, it’s not too difficult to clean your furnace burners. The following is a step-by-step guide to thoroughly clean your burners for efficient heating.

What You Need

  • Power drill
  • A flexible drill extension bit
  • Brass brush
  • Compressed air

How to Clean the Burners

  1. Turn off the power: Turn off the electricity at the breaker and the gas at the main valve.
  2. Locate your burner: Remove the furnace door. You’ll see the burners immediately or the burner box that houses the burner. If your furnace has a burner box, open the door to access the burner/s.
  3. Detach the burner: Use the power drill or a small wrench to remove the screws holding the burner in place. Then take out the burner and hold it over a trash can or a piece of newspaper.
  4. Clean the burner thoroughly: Use the brass brush to scrub the burner vigorously. Make sure to scrub along the face of each burner then along the burner length and wings.
  5. Replace the burner and test: Once you’re satisfied that you’ve scrubbed off the dirt buildup, replace the burner and tighten it into place. Then replace the furnace door/s and turn on the circuit breaker and gas valve. After that, you can test the furnace to see if it works.


Now you know how to diagnose dirty furnace burners and even clean a dirty burner. Don’t hesitate to consult an HVAC pro whenever you feel overwhelmed.